Welding monitoring apparatus and welding monitoring method

ABSTRACT

Provided is a welding monitoring apparatus that monitors a welding state of a V-convergence region in which a strip-shaped metal sheet is converged in a V-shape, when the metal sheet is cylindrically formed while being conveyed, and both side edges of the metal sheet are heated and melted in a manner of being butted each other while being converged in the V-shape, such that an electric resistance welded steel pipe is manufactured. This welding monitoring apparatus includes an image capturing unit that captures images of a region including the V-convergence region in time series; and an image processing unit that extracts a welding point based on the images captured in time series and detects the presence or absence and a position of irregular arcing at the welding point or on an upstream side of the welding point.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a welding monitoring apparatus and awelding monitoring method for an electric resistance welded steel pipe.

RELATED ART

An electric resistance welded steel pipe is manufactured through thefollowing step. That is, first, a strip-shaped metal sheet iscontinuously formed into a cylindrical shape by a roll group while beingconveyed along its longitudinal direction. Then, while an upset isapplied to the cylindrically formed metal sheet from its side by a pairof squeeze rolls, and while heat-input is controlled with respect toboth side edges in a circumferential direction of the metal sheetconverged in a V-shape, both the side edges are welded by being heatedand melted through high-frequency resistance welding or inductionheating welding and being butted each other. Since this step of weldingan electric resistance welded steel pipe is an important step whichdirectly affects the quality of an electric resistance welded steelpipe, various examinations have been performed in the related art.

For example, Patent Document 1 discloses that the form of a welding spotchanges into “a first kind”, “a second kind”, “a transition region”, or“a subordinate second kind” depending on the heat input amount appliedat the time of welding (refer to FIG. 8). This Patent Document 1 employsan electric resistance welding work management apparatus including “anarc detecting region extraction unit that extracts a narrow regionincluding a welding slit generated between a V-convergence point (VI)that is an abutment point at which the steel sheet abuts and a weldingpoint (W) in which a molten steel starts to be discharged from theinside of the steel sheet, as an arc detecting region; and an arcdetecting unit that detects an arc generated in the arc detectingregion”.

According to this constitution, it is possible to obtain a frequency ofgeneration of an arc regularly generated (which will hereinafter bereferred to as a steady state arc) on a downstream side of theV-convergence point.

Moreover, this electric resistance welding work management apparatusemploys a constitution “including an arc generation frequency measuringunit that measures a frequency of generation of an arc, and a weldingphenomenon determining unit that determines a welding phenomenon thereofbased on whether or not the frequency of generation of an arc is equalto or greater than a predetermined value”.

According to this constitution, the form of a steady state arcdownstream of the V-convergence point is grasped based on the frequencyof generation of the steady state arc, and thus an appropriate heatinput amount is controlled.

PRIOR ART DOCUMENT Patent Document

[Patent Document 1] Japanese Unexamined Patent Application, FirstPublication No. 2016-78056

According to the technology disclosed in Patent Document 1, it ispossible to realize an appropriate welding state downstream of theV-convergence point. However, from the viewpoint of improving thequality of a welding spot, further amelioration is demanded.

For example, high-frequency electric resistance welding is a technologyin which currents are concentrated on a welding surface such thatwelding is efficiently performed by utilizing a proximity effect and askin effect of steel edges in a weld. However, when high-frequencyelectric resistance welding is performed, a strong electromagnetic fieldis formed around the steel edges due to significant currents flowing inthe steel edges. Since this electromagnetic field is maximized at awelding point (V point), if a magnetic substance is present around thesteel edges, it is likely to be incorporated into the welding point.

As a material of an electric resistance welded steel pipe, sometimes asteel sheet to which scale generated at the time of hot rolling adheresis adopted, and the scale is peeled off from a surface layer through aforming process or by a fin pass roll. Particularly, the fin pass rollcan form a newly formed surface by scraping a welding surface. On theother hand, scale or iron powder may be generated. In addition, there isa possibility that iron powder may be similarly generated even in apickled material in which scale seldom adheres to its surface layer. Inthis manner, a phenomenon, in which scale that has been peeled off orscale powder, iron powder, or the like that has been scraped is caughtin a weld as a foreign substance, occurs sometimes. In this case, if aforeign substance has a large size to a certain degree, there is apossibility that it will remain on the welding surface as a solidwithout being melted until an upset is applied and it will become adefect without being discharged. Although the frequency of generation ofa defect is not high, it degrades toughness of a weld and causes a crackat the time of working. Therefore, it is strongly demanded that aforeign substance is to be detected during pipe-making regardless of itssize.

However, in the technology disclosed in Patent Document 1, the frequencyof generation of a steady state arc on a downstream side of the weldingpoint (V point) is obtained and the heat input state of welding isgrasped, but countermeasures related to generation of a defect caused bya caught-in foreign substance are not provided.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The present invention has been made in consideration of the foregoingcircumstances, and an object thereof is to provide a welding monitoringapparatus and a welding monitoring method, in which a relatively lightcaught-in defect caused by an incorporated foreign substance such asscale powder or iron powder can be detected in real time in a weldingstep of an electric resistance welded steel pipe.

Means for Solving the Problem

In order to gratify the foregoing object, first, the inventors haveanalyzed a target defect. FIG. 1A and FIG. 1B show a result obtained byinstalling an electric resistance welded steel pipe such that a weld ofa defect-generated portion is at a 90° position in a vertical direction,and performing a flattening test for reduction in the verticaldirection. FIG. 1A shows an external appearance photograph of a fracturesurface having a crack, and FIG. 1B shows a secondary electron imagecaptured by a scanning electron microscope (SEM). As shown in FIG. 1A, adefect to be regarded as a target is characterized by a slender blackstreak pattern present in a central position of the crack whileextending in the through-thickness direction and having a width ofseveral millimeters or smaller present. In the secondary electron imageshown in FIG. 1B as well, a boundary between a black streak part and thesurrounding part is manifested, and a dimple fracture surface which ischaracteristically formed in the surrounding part at the time of a lowheat input has been observed. From the results of the flattening testdescribed above, it is speculated that the defect has been generated dueto a caught-in foreign substance which has a lower temperature than awelding surface at the time of welding and causes a heat release of thesurrounding part.

Moreover, FIG. 2A and FIG. 2B show scanning electron microscope (SEM)analysis results of the black streak part. As a result of compositionanalysis of a portion 3 in FIG. 2A, in which the black streak part isenlarged, using a scanning electron microscope (SEM), the peaks of ironand oxygen are noticeable as shown in FIG. 2B. On the other hand,compositions other than both the elements are at a substantially noiselevel, and thus it is ascertained that the composition of the blackstreak part is iron oxide. When a plurality of places are analyzed, fineingots of such iron oxide are scattered inside the black streak part andare highly concentrated in their entirety. Therefore, it is determinedthat this defect is caused due to iron oxide (scale) which has beencaught in or the welding surface in which iron powder is caught in andis oxidized.

The caught-in process through which such a defect is generated has notbeen clarified until now. Therefore, an experiment in which a defect atthe time of welding was artificially generated by using scale or ironpowder was performed. At this time, a weld was cyclically image-capturedby a camera installed above the weld, and comparison was performed withrespect to a crack (that is, a defect-generated portion) generatedthrough a flattening test. As a result, it has been found that there isa possibility that a foreign substance will be carried from an upstreamside of a welding point while it adheres to the welding surface and willbe caught in. Moreover, it has been found that if welding surfaces(edges) approach each other when a foreign substance is caught in, boththe edges are short-circuited, and arcing (which will hereinafter bereferred to as irregular arcing) occurs. Therefore, the inventors haveinvented an image processing method of automatically detecting irregulararcing by utilizing the features that this irregular arcing occurs at awelding point or on an upstream side thereof.

That is, the present invention provides the following aspects.

(1) According to an aspect of the present invention, there is provided awelding monitoring apparatus that monitors a welding state of aV-convergence region in which a strip-shaped metal sheet is converged ina V-shape, when the metal sheet is cylindrically formed while beingconveyed, and both side edges of the metal sheet are heated and meltedin a manner of being butted each other while being converged in theV-shape, such that an electric resistance welded steel pipe ismanufactured. The welding monitoring apparatus includes: an imagecapturing unit that captures images of a region including theV-convergence region in time series; and an image processing unit thatextracts a welding point based on the images captured in time series anddetects the presence or absence and the position of irregular arcing ata welding point or on an upstream side of the welding point.

(2) The aspect according to (1) may be constituted as follows. Theimages captured by the image capturing unit are RGB images. The imageprocessing unit extracts at least one of a red image and a blue imagefrom the RGB images, performs inverted binarization and labeling of thered image with respect to the red image, and detects a high-luminanceportion in the blue image with respect to the blue image.

(3) In the aspect according to (1) or (2), the image capturing unit maybe a camera capturing 200 frames or more per second.

(4) In addition, according to another aspect of the present invention,there is provided a welding monitoring method for monitoring a weldingstate of a V-convergence region in which a strip-shaped metal sheet isconverged in a V-shape, when the metal sheet is cylindrically formedwhile being conveyed, and both side edges of the metal sheet are heatedand melted in a manner of being butted each other while being convergedin the V-shape, such that an electric resistance welded steel pipe ismanufactured. The welding monitoring method includes: an image capturingstep of capturing images of a region including the V-convergence regionin time series; and a detecting step of extracting a welding point basedon the images captured in time series and detecting the presence orabsence and a position of irregular arcing at the welding point or on anupstream side of the welding point.

(5) The aspect according to (4) may be constituted as follows. RGBimages are used as the images. In the detecting step, at least one of ared image and a blue image is extracted from the RGB images, invertedbinarization and labeling of the red image are performed with respect tothe red image, and a high-luminance portion in the blue image isdetected with respect to the blue image.

(6) In the aspect according to (4) or (5), in the image capturing step,images may be captured at a frame rate of 200 frames or more per second.

(7) The aspect according to any one of (4) to (6) may further include amarking step of marking the position of the irregular arcing in alongitudinal direction in the electric resistance welded steel pipe.

(8) In the case of (7), the aspect may further include a defectpresence-or-absence specifying step of performing an ultrasonic testwith respect to a region to which the marking is applied.

(9) The aspect according to any one of (4) to (6) may further include atracking step of tracking the position of the irregular arcing in alongitudinal direction in the electric resistance welded steel pipe.

As a camera to be used in the image capturing unit and the imagecapturing step, any of a monochrome camera and a color camera can beused. However, in a case where the aspects of (2) and (5) are employed,it is preferable to use a color camera which can perform colorseparation so as to distinguish light emission from a molten steel andirregular arcing from each other with high contrast.

Effects of the Invention

According to the welding monitoring apparatus and the welding monitoringmethod of each of the aspects of the present invention, it is possibleto detect a defect which is generated due to a foreign substance caughton a welding surface, including a relatively light defect. Then, thisdetection information can be tracked in a step of manufacturing anelectric resistance welded steel pipe, or marking can be performed on asteel pipe itself immediately after a defect is detected. In this case,a defect portion is unerringly eliminated from a product, so that only anormal portion having no caught-in defect can be shipped as a product.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a photograph showing an external appearance of a targetdefect.

FIG. 1B is a photograph showing a secondary electron image of a targetdefect.

FIG. 2A is a view showing an example in which qualitative analysis isperformed with respect to a target defect by using a scanning electronmicroscope (SEM), and it is a photograph of a backscattered electronimage of a scanning electron microscope (SEM).

FIG. 2B is a view showing an example in which qualitative analysis isperformed with respect to a target defect by using a scanning electronmicroscope (SEM), and it is a graph showing results of compositionanalysis of a portion 3 in FIG. 2A performed by using a scanningelectron microscope (SEM).

FIG. 3 is a perspective view showing an electric resistance welded steelpipe welding apparatus in which a welding monitoring apparatus and awelding monitoring method according to an embodiment of the presentinvention are applied.

FIG. 4 is a flowchart of an image processing algorithm for detectinggeneration of a defect by using the same welding monitoring apparatusand the same welding monitoring method.

FIG. 5 is a photograph showing an example of an image of an imageprocessing process for detecting generation of a defect. FIG. 5(a) showsa captured image, FIG. 5(b) shows a detected welding point, FIG. 5(c)shows a detected blue component, and FIG. 5(d) shows a detectedhigh-luminance portion.

FIG. 6 is a photograph in which a state of a weld at the time ofgeneration of a defect is image-captured.

FIG. 7 is a view showing an example in which a defect-generated positionand a portion where a crack is generated through a flattening test arebutted each other. FIG. 7(a) is a photograph showing an actual defectportion checked after the flattening test and the external appearancethereof, and FIG. 7(b) shows comparison between a portion whereirregular arcing has occurred and an image.

FIG. 8 is a view describing an example of a welding monitoring method inthe related art, and it is a view showing each of welding phenomena of“a first kind”, “a second kind”, “a transition region”, and “asubordinate second kind” in a welding spot.

EMBODIMENT OF THE INVENTION

An embodiment of a welding monitoring apparatus and a welding monitoringmethod for an electric resistance welded steel pipe according to thepresent invention will be described below with reference to thedrawings.

FIG. 3 shows a perspective view of an electric resistance welded steelpipe welding apparatus in which the same welding monitoring apparatusand the same welding monitoring method are applied. The same electricresistance welded steel pipe welding apparatus is an apparatus whichmanufactures an electric resistance welded steel pipe by cylindricallyforming a strip-shaped metal sheet 1 while the strip-shaped metal sheet1 is conveyed along its longitudinal direction, and heating and meltingboth side edges (edges) 1 a and 1 b of the metal sheet 1 in a manner ofbeing butted each other while the side edges are converged in a V-shapein a plan view. The reference sign 3 indicated in FIG. 3 is aV-convergence point at which both the side edges 1 a and 1 b convergedin the V-shape are butted each other and are heated and melted. In thisFIG. 3, the metal sheet (steel sheet) 1 proceeds from the front side onthe paper toward the deep side on the paper along its longitudinaldirection. Therefore, in a case where the V-convergence point 3 is takenas a reference, the front side on the paper becomes an upstream side,and the deep side on the paper becomes a downstream side.

The welding monitoring apparatus of the present embodiment monitors awelding state of a V-convergence region in which the metal sheet 1 isconverged in a V-shape, when an electric resistance welded steel pipe ismanufactured.

The reference signs 4 a and 4 b in FIG. 3 indicate a pair of contacttips disposed to come into contact with spots near both the side edges 1a and 1 b of the metal sheet 1 in the circumferential direction, whichtravels toward the V-convergence point 3. In addition, the referencesign 5 in FIG. 3 indicates an impeder which is disposed in a centralpart of the cylindrically formed metal sheet 1, and the reference sign 6indicates a high-frequency power supply which is connected to each ofthe contact tips 4 a and 4 b. High-frequency currents supplied throughthe contact tips 4 a and 4 b flow as indicated with arrows along theextending direction of both the side edges 1 a and 1 b in thecircumferential direction of the metal sheet 1, so that both the sideedges 1 a and 1 b of the metal sheet 1 are heated and melted due tohigh-frequency resistance. Similar to that in the related art, a heatinput is controlled by means of these high-frequency currents. A pair ofsqueeze rolls 2 and 2 near the V-convergence point 3 apply an upset toboth the side edges 1 a and 1 b of the metal sheet 1 which have beenheated and melted such that both the side edges 1 a and 1 b aresubjected to electric resistance welding. Instead of high-frequencyresistance welding using the contact tips 4 a and 4 b, an inductionheating-type welding in which heating is performed by using an inductioncoil can also be employed.

The squeeze rolls 2 and 2 apply an upset to both the side edges 1 a and1 b of the metal sheet 1 which have been heated and melted in thismanner, so that oxide on a surface of the metal sheet 1 is extruded anddischarged from a welding surface, and thereby excellent welding qualityis achieved. However, as described above, if a foreign substance iscaught on the welding surface, strength of the welding surface isdegraded, and a possibility of a crack at the time of working of a steelpipe or when an internal pressure is applied to a steel pipe increases.

The welding monitoring apparatus of the present embodiment includes animage capturing unit 7 and an image processing unit 8 in order tomonitor a caught-in defect in real time including a light defect whichhave not been able to be monitored in the related art. According to thiswelding monitoring apparatus, irregular arcing (arcing into which aforeign substance is incorporated) which has occurred in a weld or on anupstream side of the weld is detected, and thus a defect portion in anelectric resistance welded steel pipe can be specified. Irregular arcingdiffers from the steady state arcing described above in regard to thefollowing points. That is, steady state arcing occurs on a downstreamside of a weld (V-convergence point 3). On the other hand, irregulararcing occurs in a weld (V-convergence point 3) and on an upstream sideof a weld (V-convergence point 3). In addition, steady state arcingoccurs between a pair of end edges (edges) when an electric resistancewelded steel pipe is formed. Therefore, the material of a welded portiongenerated as a result thereof is equivalent to the base material of themetal sheet 1. In contrast, in a case of irregular arcing, it occurs dueto a foreign substance such as iron oxide (scale) or iron powder.Therefore, the material of a welded portion differs from the basematerial of the metal sheet 1.

The image capturing unit 7 captures an image of a surface of a regionincluding the V-convergence region in which both the side edges 1 a and1 b of the metal sheet 1 are converged in a V-shape. For example, a CCDcamera is used. The image capturing apparatus is disposed above a weld(V-convergence point 3) such that a range including a weld(V-convergence point 3) and the upstream side of the weld (V-convergencepoint 3) can be captured from above thereof. Since such a way ofdisposing the image capturing apparatus above is employed, for example,even in a case of being applied to a small-diameter line, the imagecapturing apparatus can be installed without hardship and withoutinterfering with other equipments (a nitrogen purge nozzle, a coolingwater piping, and the like).

In the metal sheet 1, since both the side edges 1 a and 1 b thereof areintensively heated and melted, radiant light is emitted from both theside edges 1 a and 1 b and places in the vicinity thereof. From thisradiant light, the image capturing unit 7 captures an image on a surfaceof the metal sheet 1 including red light.

FIG. 4 shows an image processing algorithm for automatically performingdetection using the image capturing unit 7 and the image processing unit8. In addition, (a) to (d) of FIG. 5 show examples of processed images.

At least one of a red component and a blue component is extracted froman RGB image (refer to (a) of FIG. 5) captured in Step S1 of FIG. 4(FIG. 4 shows an example of a case where both are extracted).

When a red component shown in Step S2 is extracted, invertedbinarization (Step S3) and labeling (Step S4) are performed to obtain awelding point in a red image, and a downstream end point in a wedge-typeregion interposed between steel edges (both the side edges 1 a and 1 b)is set as the welding point (Step S5, also refer to (b) of FIG. 5).

On the other hand, when a blue component shown in Step S6 is extracted,a blue image is subjected to binarization (Step S7, also refer to (c) ofFIG. 5) and labeling (Step S8), and a high-luminance portion is detected(Step S9, also refer to (d) of FIG. 5). In the present image in which aradiant pattern of a molten steel is captured, in a case where irregulararcing is present in spite of the low level of the blue component, theblue component exhibits high luminance and can be detected. Here, highluminance indicates a level of 200 or higher in 255 gradations, forexample. This high-luminance portion is subjected to labeling (theforegoing Step S8), and positional information is derived out. Labelingindicates processing in which the same label number is attached to onelump (blob) in a binary image, a particular blob is extracted, and theposition (the maximum point and the minimum point of the X-coordinate,and the maximum point and the minimum point of the Y-coordinate), thewidth, the length, the area, and the like of the blob within the imageare extracted. Even if a plurality of irregular arcing portions arepresent, the positional information of each thereof can be derived out.

The position of the welding point and the high-luminance portionobtained in this manner are compared to each other in Step S10. If theposition of the high-luminance portion is not on a downstream side ofthe welding point (Step S10: YES), generation of an irregular arcingportion is determined as generation of a defect (Step S11), and theprocessing returns to Step S1. On the other hand, if the position of thehigh-luminance portion is on a downstream side of the welding point(Step S10: NO), it is determined as normal (Step S12), and theprocessing subsequently returns to Step S1.

As described above, a defect can be determined at all times. Here, ablue component image is extracted and processed in order to detect anirregular arcing portion with high contrast. However, since an irregulararcing portion is also saturated (Level 255 in 255 gradations) even in ared component image with high probability, only a red component can alsobe detected.

If a camera capturing 200 frames or more per second is used when animage is captured, it is experimentally ascertained that there is noleakage in detection of an irregular arcing portion. Therefore, it ispreferable to use a camera capturing 200 frames or more per second whenan image is captured in Step S1.

Hereinafter, Examples of the present invention will be described.

EXAMPLES

In an actual manufacturing line, the positions of a welding point weremeasured while continuously capturing images of a weld and performingimage processing. The pipe adopted as a welding monitoring target was anactual pipe of φ100 mm×4 mmt. In the camera used for capturing images,the frame rate was set to 200 frames/second, and the exposure time wasset to 1/10,000 seconds.

FIG. 6 shows an example of welding monitoring. In the image of FIG. 6captured at the time of generation of a defect, when a pair of weldingsurfaces (edges) approached each other, the welding surfaces wereshort-circuited due to a foreign substance such as scale or iron powderhaving conductivity, and thus irregular arcing occurred. In places whereno foreign substance adhered, no irregular arcing occurred even when thewelding surfaces approached each other, and it could be checked that nodefect was generated.

An example in which this phenomenon and generation of a defect arebutted is shown in (a) and (b) of FIG. 7.

In (a) of FIG. 7, actual defect portions in which a crack has beengenerated after a flattening test, and photographs of the externalappearance respectively corresponding to these actual defect portionsare shown. It is ascertained that a crack has been generated in threeplaces of 0.24 m, 1.93 m, and 2.51 m from a steel pipe head. A “notch”at a position of 1.17 m indicates a portion in which a notch has beenmade in the edge in advance as a marker for tracking. This marker wasused as a reference position for specifying the position along thelongitudinal direction of the actual pipe.

In (b) of FIG. 7, among captured images, images of the portion in whichirregular arcing has occurred in the welding point or on an upstreamside thereof and the corresponding portions are butted each other areshown. An image of the marker was also able to be checked (not shown).Therefore, it is ascertained that each generation portion correspondsextremely well to the flat crack portion. Since images other than thecorresponding portions did not have irregular arcing and any otherabnormality, thereby being normal, it was actually verified thatgeneration of a defect was accompanied by irregular arcing.

The main points of the welding monitoring apparatus and the weldingmonitoring method according to the embodiment described above will besummarized below.

(1) The welding monitoring apparatus of the present embodiment monitorsthe welding state of the V-convergence region in which the strip-shapedmetal sheet 1 is converged in a V-shape, when the metal sheet 1 iscylindrically formed while being conveyed along its longitudinaldirection, and both the side edges 1 a and 1 b of the metal sheet 1 areheated and melted in a manner of being butted each other while beingconverged in the V-shape, such that an electric resistance welded steelpipe is manufactured. Then, this welding monitoring apparatus includes:the image capturing unit 7 that captures images of a region includingthe V-convergence region in time series; and the image processing unit 8that extracts a welding point based on the images captured in timeseries and detects the presence or absence and the position of irregulararcing at the welding point or on an upstream side of the welding point.

(2) The welding monitoring apparatus according to (1) is constituted asfollows. The images captured by the image capturing unit 7 are RGBimages. The image processing unit 8 extracts at least one of a red imageand a blue image from the RGB images, performs inverted binarization andlabeling of the red image with respect to the red image, and detects ahigh-luminance portion in the blue image with respect to the blue image.

(3) In the aspect according to (1) or (2), the image capturing unit is acamera capturing 200 frames or more per second.

(4) In addition, the welding monitoring method of the present embodimentis used for monitoring the welding state of the V-convergence region inwhich the strip-shaped metal sheet 1 is converged in a V-shape, when themetal sheet 1 is cylindrically formed while being conveyed along itslongitudinal direction, and both the side edges 1 a and 1 b of the metalsheet 1 are heated and melted in a manner of being butted each otherwhile being converged in the V-shape, such that an electric resistancewelded steel pipe is manufactured. This welding monitoring methodincludes: an image capturing step of capturing images of a regionincluding the V-convergence region in time series; and a detecting stepof extracting a welding point based on the images captured in timeseries and detecting the presence or absence and the position ofirregular arcing at the welding point or on an upstream side of thewelding point.

(5) In the welding monitoring method according to (4), the followingsare performed. RGB images are used as the images. In the detecting step,at least one of a red image and a blue image is extracted from the RGBimages, inverted binarization and labeling of the red image areperformed with respect to the red image, and a high-luminance portion inthe blue image is detected with respect to the blue image.

(6) In the welding monitoring method according to (4) or (5), in theimage capturing step, images are captured at a frame rate of 200 framesor more per second.

Moreover, the following steps in (7) and (8), or (9) can be performed.

(7) The welding monitoring method according to any one of (4) to (6)further includes a marking step of marking the position of the irregulararcing in the longitudinal direction in the electric resistance weldedsteel pipe.

(8) The welding monitoring method according to (7) further includes adefect presence-or-absence specifying step of performing an ultrasonictest with respect to a region to which the marking is applied.

(9) The aspect according to any one of (4) to (6) further includes atracking step of tracking the position of the irregular arcing in thelongitudinal direction in the electric resistance welded steel pipe.

According to the welding monitoring apparatus and the welding monitoringmethod described above, the presence or absence of a caught-in defectcan be easily detected in real time by extracting a welding point andautomatically determining the presence or absence of generation ofirregular arcing in the vicinity of the welding point or on an upstreamside of the welding point. Then, product-tracking is performed or asteel pipe is subjected to marking in the vicinity of the squeeze rolls2 immediately after irregular arcing is detected, based on theinformation of the presence or absence of generation of irregulararcing, so that the position of a defect-generated portion is clarified,and thus the defect-generated portion can be easily eliminated in arefining step. Therefore, only a normal portion including no defect canbe shipped as a product.

INDUSTRIAL APPLICABILITY

According to the present invention, it is possible to provide a weldingmonitoring apparatus and a welding monitoring method, in which arelatively light caught-in defect caused by an incorporated foreignsubstance such as scale powder or iron powder can be detected in realtime in a welding step of an electric resistance welded steel pipe.

BRIEF DESCRIPTION OF THE REFERENCE SYMBOLS

-   -   1: metal sheet    -   1 a, 1 b: both side edges of metal sheet    -   2: squeeze roll    -   3: welding point    -   4 a, 4 b: contact tip    -   5: impeder    -   6: high-frequency power supply    -   7: image capturing unit    -   8: image processing unit

1. A welding monitoring apparatus that monitors a welding state of aV-convergence region in which a strip-shaped metal sheet is converged ina V-shape, when the metal sheet is cylindrically formed while beingconveyed, and both side edges of the metal sheet are heated and meltedin a manner of being butted each other while being converged in theV-shape, such that an electric resistance welded steel pipe ismanufactured, the apparatus comprising: an image capturing unit thatcaptures images of a region including the V-convergence region in timeseries; and an image processing unit that extracts a welding point basedon the images captured in time series and detects the presence orabsence and a position of irregular arcing at the welding point or on anupstream side of the welding point.
 2. The welding monitoring apparatusaccording to claim 1, wherein the images captured by the image capturingunit are RGB images, and wherein the image processing unit extracts atleast one of a red image and a blue image from the RGB images, performsinverted binarization and labeling of the red image with respect to thered image, and detects a high-luminance portion in the blue image withrespect to the blue image.
 3. The welding monitoring apparatus accordingto claim 1, wherein the image capturing unit is a camera capturing 200frames or more per second.
 4. A welding monitoring method for monitoringa welding state of a V-convergence region in which a strip-shaped metalsheet is converged in a V-shape, when the metal sheet is cylindricallyformed while being conveyed, and both side edges of the metal sheet areheated and melted in a manner of being butted each other while beingconverged in the V-shape, such that an electric resistance welded steelpipe is manufactured, the method comprising: an image capturing step ofcapturing images of a region including the V-convergence region in timeseries; and a detecting step of extracting a welding point based on theimages captured in time series and detecting the presence or absence anda position of irregular arcing at the welding point or on an upstreamside of the welding point.
 5. The welding monitoring method according toclaim 4, wherein RGB images are used as the images, and wherein in thedetecting step, at least one of a red image and a blue image isextracted from the RGB images, inverted binarization and labeling of thered image are performed with respect to the red image, and ahigh-luminance portion in the blue image is detected with respect to theblue image.
 6. The welding monitoring method according to claim 4,wherein in the image capturing step, images are captured at a frame rateof 200 frames or more per second.
 7. The welding monitoring methodaccording to claim 4, further comprising: a marking step of marking theposition of the irregular arcing in a longitudinal direction in theelectric resistance welded steel pipe.
 8. The welding monitoring methodaccording to claim 7, further comprising: a defect presence-or-absencespecifying step of performing an ultrasonic test with respect to aregion to which the marking is applied.
 9. The welding monitoring methodaccording to claim 4, further comprising: a tracking step of trackingthe position of the irregular arcing in a longitudinal direction in theelectric resistance welded steel pipe.
 10. The welding monitoringapparatus according to claim 2, wherein the image capturing unit is acamera capturing 200 frames or more per second.
 11. The weldingmonitoring method according to claim 5, wherein in the image capturingstep, images are captured at a frame rate of 200 frames or more persecond.
 12. The welding monitoring method according to claim 5, furthercomprising: a marking step of marking the position of the irregulararcing in a longitudinal direction in the electric resistance weldedsteel pipe.
 13. The welding monitoring method according to claim 6,further comprising: a marking step of marking the position of theirregular arcing in a longitudinal direction in the electric resistancewelded steel pipe.
 14. The welding monitoring method according to claim5, further comprising: a tracking step of tracking the position of theirregular arcing in a longitudinal direction in the electric resistancewelded steel pipe.
 15. The welding monitoring method according to claim6, further comprising: a tracking step of tracking the position of theirregular arcing in a longitudinal direction in the electric resistancewelded steel pipe.
 16. The welding monitoring method according to claim11, further comprising: a marking step of marking the position of theirregular arcing in a longitudinal direction in the electric resistancewelded steel pipe.
 17. The welding monitoring method according to claim16, further comprising: a defect presence-or-absence specifying step ofperforming an ultrasonic test with respect to a region to which themarking is applied.
 18. The welding monitoring method according to claim11, further comprising: a tracking step of tracking the position of theirregular arcing in a longitudinal direction in the electric resistancewelded steel pipe.
 19. The welding monitoring method according to claim12, further comprising: a defect presence-or-absence specifying step ofperforming an ultrasonic test with respect to a region to which themarking is applied.
 20. The welding monitoring method according to claim13, further comprising: a defect presence-or-absence specifying step ofperforming an ultrasonic test with respect to a region to which themarking is applied.